1. Field of the Invention
The present invention relates to a refrigerant composition which is suitable for an ultralow-temperature refrigerator using a non-azeotropic mixed refrigerant and is free of a possibility of causing depletion of the ozone layer.
2. Description of the Related Art
Heretofore, a refrigerator using a non-azeotropic mixed refrigerant achieves ultralow temperatures by condensing refrigerants having lower boiling points in succession by evaporation of refrigerants having higher boiling points and a low-temperature refrigerant returning from the last evaporator so as to evaporate a refrigerant having the lowest boiling point at the end.
The present inventor has proposed examples of such a refrigerator and a refrigerant composition in Japanese Patent Publication No. 55944/1994.
However, since the refrigerant uses HCFC, it may cause depletion of the ozone layer.
Accordingly, the development of an alternate refrigerant composition which is free from a possibility of causing depletion of the ozone layer and capable of maintaining the performance of a conventional refrigerating circuit without modifying the circuit is desired.
Under the circumstances, the present applicant has proposed a refrigerant composition comprising R600 (n-butane: H3CH2CH2CH3), R125 (CHF2CF3), R23 (trifluoromethane: CHF3) and R14 (tetrafluoromethane: CF4) in Japanese Patent Application No. 526882/2001. However, since this refrigerant composition uses R600 which is combustible, it may burn upon leakage. It is better to avoid use of a combustible material on as many occasions as possible.
The present invention provides a refrigerant composition which hardly burns upon leakage and is free from a possibility of causing depletion of the ozone layer, and a refrigerating circuit using the refrigerant composition.